The central focus of this program continues in the direction of cellular mechanisms of muscle contraction. However, some specific concentrations of effort have developed in some of the projects. Project I now focuses more specifically on the localization and binding of Ca ions in the cardiac cell coat (Langer, Frank) and the role of nitrogen metabolism. Project II is concentrating on the measurement of force and control of length change in single myocardial fibers (Brady, Roos) with a continuing effort in attempts to relate the kinetics of mechanical transients to biochemical rate constants (Yeatman, Brady). The objectives of Project III continue in their original direction, emphasizing mechanochemical transformation (Homsher).